Output circuit for audio codec chip

ABSTRACT

An output circuit for audio codec chip includes a noise eliminating circuit electrically coupled to the audio codec chip for eliminating noise signals. The noise eliminating circuit includes a first switch and a second switch. When the audio codec chip output signals jump from low voltage level to high voltage level, the noise signals are grounded via the first and second switches respectively.

BACKGROUND

1. Technical Field

The present disclosure relates to output circuits, and particularly toan output circuit for an audio codec chip.

2. Description of Related Art

In computer systems, audio codec chips are positioned on themotherboards for outputting and receiving audio signals. A typical audiocodec chip is electrically coupled to and communicates with a pluralityof peripheral devices directly, e.g. speaker, earphone, and so on.However, when the computer system is awakened from the sleep mode, theaudio codec chip output signals jump from low voltage level to highvoltage level, e.g. increases from 0 volt to 2.5 volts. This rapidvoltage level change has a remarkable influence on the peripheraldevices, and generates large amounts of noise signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a block diagram of an output circuit for an audio codec chip,in accordance with an embodiment.

FIG. 2 is a circuit diagram of the output circuit for the audio codecchip of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1 and FIG. 2, an output circuit for an audio codecchip 10 includes a noise eliminating circuit 20 and a peripheral device30. The audio codec chip 10 includes an L-channel analog signal outputterminal 11 and an R-channel analog signal output terminal 12. Theperipheral device 30 includes an L-channel analog signal input terminal31 and an R-channel analog signal input terminal 32. The L-channelanalog signal output terminal 11 is electrically coupled to theL-channel analog signal input terminal 31 via the noise eliminatingcircuit 20. The R-channel analog signal output terminal 12 iselectrically coupled to the R-channel analog signal input terminal 32via the noise eliminating circuit 20. In one embodiment, the peripheraldevice 30 is a speaker.

The noise eliminating circuit 20 includes a first capacitor C1, a secondcapacitor C2, a third capacitor C3, a first resistor R1, a secondresistor R2, a third resistor R3, a fourth resistor R4, a first switchT1, a second switch T2 and a third switch T3. The first and secondswitches T1, T2 are NPN type transistors, the third switch T3 is a PNPtype transistor.

The first switch base is electrically coupled to the third switchcollector. The first switch collector is electrically coupled to thesecond capacitor first terminal. The second capacitor second terminal iselectrically coupled to the R-channel analog signal output terminal 12.The first switch emitter is grounded. The first switch emitter iselectrically coupled to the third resistor first terminal. The thirdresistor second terminal is electrically coupled to the first switchcollector. The second switch base is electrically coupled to the thirdswitch collector. The second switch collector is electrically coupled tothe first capacitor first terminal. The first capacitor second terminalis electrically coupled to the L-channel analog signal output terminal11. The second switch emitter is grounded. The second switch emitter iselectrically coupled to the fourth resistor first terminal. The fourthresistor second terminal is electrically coupled to the second switchcollector. The third switch base is electrically coupled to the firstresistor first terminal. The third switch emitter is electricallycoupled to the second resistor first terminal. The first resistor secondterminal and the second resistor second terminal respectively receive a+5 volts voltage. The third switch emitter is electrically coupled tothe third capacitor first terminal. The third capacitor second terminalis grounded.

In use, when the computer system is awakened from the sleep mode, theL-channel and R-channel analog signal output terminals 11, 12 outputsignals jump from 0 volts to 2.5 volts. The third switch T3 receives the+5 volts voltage and is turned on. The +5 volts voltage is provided tothe first and second switches bases respectively. The normal audiosignals from the audio codec chip 10 are at a low voltage level. Thefirst and second switches collectors receive the low voltage level andare turned off. Therefore, the normal audio signals from the L-channeland R-channel analog signal output terminals 11, 12 can be transmittedto the peripheral device 30 via the first and second capacitors C1, C2respectively. The noise signals from the audio codec chip 10 are at ahigh voltage level. The first and second switches collectors receive thehigh voltage level and are turned on. Therefore, the noise signals fromthe L-channel and R-channel analog signal output terminals 11, 12 can begrounded via the first and second switches T1, T2 respectively.

It is to be understood, however, that even though numerouscharacteristics and advantages of the embodiments have been set forth inthe foregoing description, together with details of the structure andfunction of the embodiments, the disclosure is illustrative only, andchanges may be made in detail, especially in matters of shape, size, andarrangement of parts within the principles of the invention to the fullextent indicated by the broad general meaning of the terms in which theappended claims are expressed.

What is claimed is:
 1. An output circuit for audio codec chip,comprising: a noise eliminating circuit electrically coupled to theaudio codec chip for eliminating noise signals; the noise eliminatingcircuit comprising a first switch and a second switch, wherein when theaudio codec chip output signals jump from low voltage level to highvoltage level, the noise signals are grounded via the first and thesecond switches respectively; wherein the audio codec chip comprises anL-channel analog signal output terminal and an R-channel analog signaloutput terminal; the L-channel and the R-channel analog signal outputterminals are grounded via the first and the second switchesrespectively; the noise eliminating circuit further comprises a firstcapacitor and a second capacitor; the L-channel analog signal outputterminal is electrically coupled to the first capacitor first terminal;the first capacitor second terminal is electrically coupled to the firstswitch; the R-channel analog signal output terminal is electricallycoupled to the second capacitor first terminal; and the second capacitorsecond terminal is electrically coupled to the second switch; the noiseeliminating circuit further comprises a third switch; and the first andsecond switches receive an input voltage via the third switch; thefirst, the second and the third switches are transistors; the firstswitch base is electrically coupled to the third switch collector; thefirst switch collector is electrically coupled to the second capacitorfirst terminal; the second capacitor second terminal is electricallycoupled to the R-channel analog signal output terminal; and the firstswitch emitter is grounded; the first and the second switches are NPNtype transistors; and the third switch is a PNP type transistor.
 2. Anoutput circuit for audio codec chip, comprising: a noise eliminatingcircuit electrically coupled to the audio codec chip for eliminatingnoise signals; the noise eliminating circuit comprising a first switchand a second switch, wherein when the audio codec chip output signalsjump from low voltage level to high voltage level, the noise signals aregrounded via the first and the second switches respectively; wherein theaudio codec chip comprises an L-channel analog signal output terminaland an R-channel analog signal output terminal; the L-channel and theR-channel analog signal output terminals are grounded via the first andthe second switches respectively; the noise eliminating circuit furthercomprises a first capacitor and a second capacitor; the L-channel analogsignal output terminal is electrically coupled to the first capacitorfirst terminal; the first capacitor second terminal is electricallycoupled to the first switch; the R-channel analog signal output terminalis electrically coupled to the second capacitor first terminal; and thesecond capacitor second terminal is electrically coupled to the secondswitch; the noise eliminating circuit further comprises a third switch;and the first and second switches receive an input voltage via the thirdswitch; the first, the second and the third switches are transistors;the first switch base is electrically coupled to the third switchcollector; the first switch collector is electrically coupled to thesecond capacitor first terminal; the second capacitor second terminal iselectrically coupled to the R-channel analog signal output terminal, andthe first switch emitter is grounded; the second switch base iselectrically coupled to the third switch collector; the second switchcollector is electrically coupled to the first capacitor first terminal;the first capacitor second terminal is electrically coupled to theL-channel analog signal output terminal; and the second switch emitteris grounded; the third switch base is electrically coupled to a firstresistor first terminal; the third switch emitter is electricallycoupled to a second resistor first terminal; and the first resistorsecond terminal and the second resistor second terminal receive theinput voltage.
 3. The output circuit for audio codec chip of claim 2,wherein the noise eliminating circuit further comprises a thirdresistor, a fourth resistor and a third capacitor; the first switchemitter is electrically coupled to the third resistor first terminal;the third resistor second terminal is electrically coupled to the firstswitch collector; the second switch emitter is electrically coupled tothe fourth resistor first terminal; the fourth resistor second terminalis electrically coupled to the second switch collector; the third switchemitter is electrically coupled to the third capacitor first terminal;and the third capacitor second terminal is grounded.
 4. An outputcircuit for audio codec chip, comprising: a noise eliminating circuitelectrically coupled to the audio codec chip for eliminating noisesignals; the noise eliminating circuit comprising a first switch and asecond switch, wherein when the audio codec chip output signals jumpfrom low voltage level to high voltage level, the noise signals aregrounded via the first and the second switches respectively; wherein theaudio codec chip comprises an L-channel analog signal output terminaland an R-channel analog signal output terminal; the L-channel and theR-channel analog signal output terminals are grounded via the first andthe second switches respectively; the noise eliminating circuit furthercomprises a first capacitor and a second capacitor; the L-channel analogsignal output terminal is electrically coupled to the first capacitorfirst terminal; the first capacitor second terminal is electricallycoupled to the first switch; the R-channel analog signal output terminalis electrically coupled to the second capacitor first terminal; and thesecond capacitor second terminal is electrically coupled to the secondswitch; the noise eliminating circuit further comprises a third switch;and the first and second switches receive an input voltage via the thirdswitch; and the input voltage is +5 volts.